Sudden behavorial change

This is my first post, and I'm looking for some help concerning my two cats, Tuesday and Oscar.

Tuesday is a female, 11 years old, spayed. Oscar is a male, 2.5 years old, neutered. Both are indoor cats, and current on shots.

Friday, I came home from work for lunch, and the cats were behaving normally.

When I came home from work a few hours later, Oscar and Tuesday were screaming bloody murder. They weren't playing, or even having a minor spat. Oscar chased Tuesday into the basement, where they fought so hard it disconnected the hose on the back of my dryer.

I've never seen them behave this way. They've co-existed peacefully for two years. I was terrified, and I seperated the two cats, keeping Tuesday in the basement and Oscar upstairs. I checked both for wounds, but could find none.

A few hours later, after Tuesday had calmed down, I let her back upstairs, when she and Oscar almost immediately went at it again.

When my fiance got home, we gave them baths, hoping that maybe if one had an odd scent, that could help normalize it. Of course, that didn't help.

Speaking with some people, one thought is that Tuesday, who is aging, is experience a sickness or kidney failure, and Oscar is sensing the weakness, and trying to establish dominance. I'm taking Tuesday to the vet on Monday (today being saturday) to have her checked out.

I have two questions, and will accept any advice offered.

1. Assuming Tuesday is healthy, how should I go about re-acclimating the two? Is that even possible? I've seen indor cats swipe, fight, but never like this. I really think they're trying to kill each other.

2. Any ideas on what could onset the suddeness of this behavior, aside from sickness? It really strikes me as bizarre, and frankly, its keeping me quite worried.

Thanks in advance for any advice and help.

Hi, welcome to TCS! Sorry about the problems that Tuesday and Oscar are having, and I don't blame you for being worried.

Even though the fighting may have been a one-time or two-time thing, anytime there is a behavioral change, especially in an older cat, a vet visit is pretty much mandatory. So it's nice that you're already aware of that.

No doubt other members will be along soon with more in-depth answers and ideas, but here are my brief thoughts with regard to your questions (and keep in mind that I am not an expert):

1) Yes, a re-introduction is possible, and I would recommend it. Especially since a few hours of solitude didn't improve matters (though since they were fighting so viciously a few days of separation might have been better than just a few hours). If you enter the Behavior forum and then use the Search this Forum function located above the list of posts, you will find a lot of useful information. You'll see the same advice given over and over again, because it has the best chance of success.

2) Tuesday possibly being sick is certainly one potential reason for the fighting. Cats have extraordinary senses and Oscar may sense that something is not right with Tuesday. She might smell differently, for instance, as a result of an illness and cats are highly reliant on their sense of smell. His actions aren't necessarily an attempt to assert dominance, however. Anyway, if she is indeed ill, hopefully the vet visit will reveal what the problem is and you and your cats will be on the road to normalcy.

It's also possible that this was an example of redirected aggression. Are there stray cats near your property? Either or both of your cats might have gotten very agitated at seeing a stray cat on their territory through a window. Since neither cat could take their frustrations out on the offending cat, they attacked the cat that was available. This is a common reaction in situations like this.

I'm sure there are other possible explanations but these are the two that immediately came to my mind.

Please keep us posted on any new developments.